Mobile radio communications system

ABSTRACT

A mobile radio communications system having a plurality of base stations accommodating a plurality of mobile stations through radio transmission channels, each of the base stations being connected to a mobile communications exchanger through a plurality of signal lines. Each of the base stations is provided therein with a signal line allocating function unit for selecting a particular signal line from a plurality of signal lines and for allocating a communication slot for a mobile station dominated by the base station at a particular slot position on the selected signal line, a radio channel allocating function unit for allocating a communication slot for the mobile station dominated by the base station at a particular slot position on a radio transmission channel at a particular frequency, and a radio signal delay control unit for performing delay control for a timing at which the base station transmits a radio signal to the mobile station dominated by the base station.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a mobile radio communicationssystem which realizes the utilization of public communication networkswith mobile stations.

[0002] Conventionally, the personal handy phone system (PHS) regarded asa type of mobile radio communications systems has a problem that a cell,i.e., a radio zone covered by a base station is so small that a handoveroperation for switching from one cell to another is frequently performedduring the high speed movement of a user making a call with a mobilestation, whereby the call is temporarily interrupted for several secondsevery time the handover operation is performed, thus largely affectingthe degradation of communication quality.

[0003] Communications systems for the personal handy phone system-havebeen described in an article “Trends of Digital Cordless Telephones”(Transactions of the Institute of Electronics, Information andCommunication Engineers, Vol. 77, No. 6, pp 636-642) about a concept oftechnical specifications for the systems.

[0004] In a personal handy phone system for public communications, eachmobile station, when moving from one radio zone to another,automatically re-initiates a call in the destination radio zone, thusautonomously realizing the handover operation only by a normal calloperation, without any particular intervening handover related operationfrom the network side. The first edition of the second-generationcordless telephone system standard (RCR STD-28) published by Radio WaveSystem Development Center Foundation (RCR) defines that the personalhandy phone systems for public communications shall employ theabove-mentioned re-call handover operation scheme.

[0005] The employment of the re-call handover operation scheme enablesmobile stations to switch a radio zone only with a normal call operationwithout any particular operational intervention from the network side,thus providing a simplified handover operation. However, a mobilestation needs to re-initiate a call in a destination radio zone everytime it performs a handover operation as it is moving from a radio zoneto another, so that the communication is interrupted during a handoveroperation for a time period required for the re-initiation which maydelay several seconds. Since a radio zone coverage is quite small in thepersonal handy phone system, if a call is being made while moving at aspeed higher than a slow speed of a vehicle, the handover operation willbe repeated so frequently that interruptions of a call, caused by thehandover operation, will occur at short intervals to an innegligibledegree.

[0006] Assume for example that a mobile station is moving at 60kilometers per hour (km/h), and a radio zone covered by a base stationhas a diameter of approximately 100 meters (m). A simple calculationbased on these assumed values shows that the handover operation isperformed every six seconds, and a call is interrupted for severalseconds at each handover operation, thus presenting a problem that aprecise communication quality cannot be ensured.

[0007]FIG. 1 illustrates an example of the configuration of aconventional personal handy phone system for showing how the position ofa communication slot transits on signal lines (500) and on radiotransmission channels (300 a)-(300 c) when the handover operation isperformed each time a mobile station (100) moves from a radio zone to anadjacent radio zone.

[0008] In the conventional personal handy phone system as illustrated,when the mobile station (100) under communication is moving from a radiozone (200 a) to an adjacent radio zone (200 b) and further to anotherradio zone (200 c) covered by respective base stations (400 a)-(400 c)in succession, the mobile station (100) re-initiates a call to a mobilecommunications exchanger (600) through a corresponding base station (400a)-(400 c) forming the radio zone (200 a)-(200 c), each time the mobilestation (100) enters a new radio zone (200 a)-(200 c), to carry out thehandover operation. Since a call is again set each time the mobilestation (100) moves from the radio zone (200 a) to (200 b) and from (200b) to (200 c), the position of the communication slot for this call isdifferent on the signal lines (500) and on the radio transmissionchannels (300 a)-(300 c) in the respective base stations (400 a)-(400c).

[0009] A technique for switching a pertinent radio zone withoutperforming the handover operation as a mobile station moves from a radiozone to another may be represented by a communications system adapted bythe Japanese Shinkansen for its transportation service and publictelephone service. However, since the network side detects movements ofrespective trains from one radio zone to next and realizes the switchingof the radio zones by the control performed on the network side, amovement detecting means and a radio zone switching control means arerequired on the network side. While the provision of these means iseffective in a system having a relatively small number of base stations,a system employing a concentrated control scheme for the radio zoneswitching, or the like, it is difficult to apply the same to thepersonal handy phone system which includes a large number of basestations, each of which autonomously performs the radio zone switching.

SUMMARY OF THE INVENTION

[0010] The present invention has been made in view of the problemsmentioned above, and its principal object is to reduce the number oftimes the handover operation is performed in a fast moving mobilestation to reduce the occurrence of call interruptions caused by thehandover operation, thus ensuring a precise communication quality forsuch a fast moving mobile station in a mobile radio communicationssystem.

[0011] To achieve the above object, the present invention provides amobile radio communications system having a function of autonomouslyswitching a base station connected to a fast moving mobile station undercommunication among base stations installed along a moving route of themobile station in succession without performing an handover operation,thus making it possible to reduce the frequency of occurrence of thehandover operation in the fast moving mobile station undercommunication.

[0012] Means for solving the problem of the present invention aredescribed in detail as follows.

[0013] According to the present invention, there is provided a mobileradio communications system having a plurality of base stationsaccommodating a plurality of mobile station through radio transmissionchannels, each mobile station connected with a mobile communicationsexchanger through a plurality of signal lines, each of the signal linesparallelly connected to the plurality of base stations, each basestation including a mechanism of selecting a particular signal line fromthe plurality of signal lines and allocating a communication slot for amobile station dominated by the base station at a particular slotposition on the selected signal line, and a mechanism of allocating acommunication slot for the mobile station dominated by the base stationat a particular slot position of a radio transmission channel at aparticular frequency, wherein each base station autonomously allocates afrequency of a radio transmission channel and a time slot on the radiotransmission channel used by a mobile station dominated by the basestation, when the mobile station was dominated by an adjacent basestation, for the mobile station dominated by the base station, inaccordance with a lapse of a fixed time period calculated from apreviously assumed moving speed of a moving mobile station undercommunication, each base station allocates a signal line and acommunication slot on the signal line used by the mobile stationdominated by the base station, when the mobile station was dominated bythe adjacent base station, for the mobile station dominated by the basestation, and the moving mobile station autonomously switches a base,station to which the moving mobile station is connected, successivelyamong the plurality of base stations installed along a moving directionof the moving mobile station under communication, without interventionof operations on the network side and without performing a handoveroperation.

[0014] According to the present invention, there is provided the mobileradio communications system characterized in that each base stationfurther comprises radio signal delay control means capable of Variablysetting a delay time for a transmission timing when each base stationtransmits a signal to a mobile station accommodated in an associatedradio zone associated with the base station, so that when the respectivebase stations transmit digital modulated signals to a mobile station,the respective base stations mutually match the phases of theirtime-division multiplexed channel slots allocated for time-divisionmultiplexed digital modulated signals sent from the respective basestations onto associated radio transmission channels and transmitted tothe mobile station.

[0015] According to the configuration of the present invention describedabove, a base station connected to a fast moving mobile station undercommunication is autonomously switched among base stations installedalong a moving route of the mobile station in succession withoutperforming an handover operation to suppress the occurrence of thehandover operation in the fast moving mobile station undercommunication, thereby making it possible to reduce the occurrence ofcall interruptions caused by the handover operation and to ensure aprecise communication quality for the fast moving mobile station in themobile radio communications system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a diagram illustrating the configuration of aconventional personal handy phone system and a concept of the handoveroperation;

[0017]FIG. 2 is a diagram illustrating the configuration of a personalhandy phone system according to the present invention and a concept of aradio zone switching operation;

[0018]FIG. 3 is a functional block diagram schematically illustrating aninternal configuration of a base station in the personal handy phonesystem according to the present invention;

[0019]FIG. 4 is a diagram illustrating changes of the position of acommunication slot for a mobile station, in the process of time, onradio transmission channels in respective radio zones in one embodimentof the personal handy phone system according to the present invention;

[0020]FIG. 5 is a diagram illustrating changes, in the process of time,of the position of a communication slot for a mobile station occupyingon a signal line in the respective base stations in one embodiment ofthe personal handy phone system according to the present invention;

[0021]FIG. 6 shows a comparison between a conventional system and thesystem according to the present invention in terms of a radio zoneswitching processing sequence; and

[0022]FIG. 7 represents an exemplary flow of operations performed byeach base station in the personal handy phone system according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will hereinafter be described withreference to one embodiment.

[0024]FIG. 2 illustrates the configuration of one embodiment of apersonal handy phone system according to the present invention and anexample of how the position of a communication slot transits on a signalline (500) and on radio transmission channels (300 a)-(300 c) due to ahandover operation caused by a movement of a mobile station (100).

[0025] As illustrated in FIG. 2, the mobile radio communications systemof the embodiment comprises a plurality of base-stations (400 a)-(400 c)which accommodate mobile stations (100 a 1)-(100 a 3) existing in radiozones (200 a)-(200 c) through radio transmission channels (300 a)-(300c), wherein the respective base stations (400 a)-(400 c) are parallellyconnected to a mobile communications exchanger (600) through a pluralityof signal lines (500), each of which is connected to corresponding oneof the plurality of mobile stations (400 a)-(400 c).

[0026] More specifically, in the personal handy phone system illustratedas an embodiment, each of the plurality of base stations (400 a)-(400 c)has a function of transmitting and receiving radio signals to and from aplurality of mobile stations (100); a function of modulating anddemodulating radio signals transmitted to and received from theplurality of mobile stations (100); a function of performing delaycontrol for the timing of transmitting signals to mobile stations (100)dominated thereby through the radio transmission channels (300 a)-(300c); a function of selecting a particular frequency for an associatedradio transmission channel, through which radio signals are transmittedto and received from the mobile station (100), and allocatingcommunication slots at particular slot positions on the radiotransmission channels (300 a)-(300 c) for the mobile stations (100)dominated thereby; and a function of selecting a particular signal line(500) from the plurality of signal lines (500) through which digitalsignals are transmitted to and received from the mobile communicationsexchanger (600), and allocating a communication slot for each of themobile station (100) dominated thereby at a particular slot position onthe selected signal line (500).

[0027] In one embodiment of the personal handy phone system according tothe present invention, as the moving mobile station (100) undercommunication is successively moving from the radio zone (200 a) to theradio zone (200 b) and to the radio zone (200 c), covered by therespective base stations (400 a) (400 c), the respective base stations(400 a)-(400 c) autonomously allocate the frequency of the radiotransmission channels (300 a)-(300 c) and the same time slot on theradio communication channels (300 a)-(300 c), used by the mobile station(100) when it was dominated by the preceding base stations (400 a)-(400c), to the mobile station (100) in the radio zones (200 a)-(200 c)covered thereby, in accordance with a fixed time calculated from apreviously assumed moving speed of the moving mobile station (100) undercommunication. Also, the respective base stations (400 a)-(400 c)allocate the same signal line (500) and the same communication slot onthe signal line (500), used by the mobile station (11) when it wasdominated by the preceding base stations (400 a)-(400 c), to the mobilestation (100) on the signal lines (500) between the base stations (400a)-(400 c) and the mobile communications exchanger (600). In this way,the position of the communication slot used by the mobile station (100)is the same on the signal line (500) and the radio communicationchannels (300 a)-(300 c) while the mobile station (100) moves from thebase station (400 a) to the base station (400 b) and further to the basestation (400 c), as illustrated in FIG. 2. This operation realizes theswitching of a radio zone to which the mobile station (100) belongs,without performing any handover operation or without any intervention ofcontrol operations on the network side.

[0028]FIG. 3 schematically illustrates the configuration of internalfunctional blocks of the base stations (400 a)-(400 c). Each of the basestations (400 a)-(400 c) is composed of an antenna (410), a radio signaltransmitter/receiver unit (420), a modulator/demodulator unit (430), aradio signal delay control unit (440), a radio channel allocatingfunction unit (450), a signal line allocating function unit (460), and acontrol unit (470) for generally controlling these functional blocks.

[0029] The radio channel allocating function unit (450), operable underthe control of the control unit (470), has a function of selecting aparticular frequency for an associated radio transmission channel (300a)-(300 c) on which radio signals are transmitted to and received from amobile station (100), and of allocating a communication slot at aparticular slot position on the associated radio transmission channel(300 a)-(300 c) for the mobile station (100) dominated by an associatedbase station (400 a)-(400 c).

[0030] The signal line allocating function unit (460), operable underthe control of the control unit (470), has a function of selectingparticular one from the plurality of signal lines (500) as a signal line(500) through which digital signals are transmitted to and received fromthe mobile communications exchanger (600), and of allocating acommunication slot on a particular slot position on the selected signalline (500) for a mobile station (100) dominated by the associated basestation.

[0031] The radio signal delay control unit (440) has a function ofproviding a transmission timing with a delay of a previously set time,when a digital signal received from the mobile communications exchanger(600) destined to a mobile station (100) dominated by an associated basestation is modulated by the modulator/demodulator unit (430) andtransmitted by the radio signal transmitter/receiver unit (420) to themobile station (100) dominated by the associated base station throughthe antenna (410).

[0032] Next, the processing of the system according to this embodimentwill be generally described with reference again to FIGS. 2 and 3.

[0033] Assuming that a mobile station (100) under communication locatedin a radio zone (200 a) formed by a base station (400 a) is moving toanother radio zone (200 b) and further to a radio zone (200 c) insuccession at a high speed. At the timing an estimated moving time ofthe mobile station (100) to the radio zone (200 b) has elapsed, afrequency and a communication slot occupied by the mobile station (100)for transmission and reception on the radio transmission channel (300 a)of the preceding base station (400 a) are also allocated as a frequencyand a communication slot for the mobile station (100) on the radiotransmission channel (300 b) of the adjacent base station (400 b) whichexists in the middle of the moving route of the mobile station (100). Inaddition, a communication slot on the signal line (500) occupied by themobile station (100) when dominated by the base station (400 a) is alsoused in the adjacent base station (400 b) which exists in the middle ofthe moving route of the mobile station (100). At this time, thepreceding base station (400 a) releases the communication slot on theradio transmission channel (300 a) and the communication slot on thesignal line (500) occupied by the mobile station (100) for anothermobile station.

[0034] For the estimation of the moving time of the mobile station (100)from the radio zone (200 a) to the radio zone (200 c), a fixed valuesuitable for an environment to which the personal handy phone systemaccording to the present invention is applied is assumed, and aparticular fixed value is previously calculated as an estimated value ofthe moving time from intervals at which base stations (400 a)-(400 c)are installed in the environment to which the personal handy phonesystem is applied and the assumed moving speed value of the mobilestation (100). For example, when the personal handy phone systemaccording to the present invention is applied to highways, a fixed valueof 80 km/h is assumed as a moving speed of a mobile station (100). Andassuming also that base stations (400 a), (400 b), (400 c) are installedat intervals of 200 m on the highways, an estimated value of a movingtime of the mobile station (100) between the radio zones (200 a) and(200 b) or (200 b) and (200 c) is calculated as 200 m÷80km/h=approximately 9 seconds.

[0035] In this way, by allocating communication slots on the signal line(500) and-on the radio transmission channels (300 a)-(300 c) inaccordance with the estimated moving time of the mobile station (100)between the radio zones (200 a) and (200 b), the mobile station (100)can continue a communication without performing the re-call handoveroperation or without requiring the intervention of control operations onthe network side, when the mobile station (100) moves from the precedingradio zone (200 a) to the adjacent radio zone (200 b). A transfer of thecommunication slot on the radio transmission channels (300 a)-(300 c) inthe radio zones (200 a)-(200 c) is realized by the operations performedby the radio channel allocating function unit (450) in the precedingbase station (400 a) and by the radio channel allocating function unit(450) in the adjacent or destination base station (400 b), while atransfer of the communication slot on the signal line (500) between thebase stations (400 a) and (400 b), and (400 b) and (400 c) is realizedby the operations performed by the signal line allocating function unit(460) in the preceding base station (400 a) and by the signal lineallocating function unit (460) in the destination or adjacent basestation (400 b).

[0036] In this way, between the adjacent base stations (400 a) and (400b), and (400 b) and (400 c), existing in the middle of the moving routeof the mobile station (100), in accordance with the estimated movingtime of the mobile station (100) from the radio zone (200 a) to theradio zone (200 c), a communication slot for the mobile station (100) issuccessively transferred on the radio transmission channels (300 a)-(300c) from the radio zone (200 a) to the radio zone (200 b) and from theradio zone (200 b) to the radio zone (200 c), and a communication sloton the signal line (500) is successively transferred from the basestation (400 a) to the base station (400 b) and from the base station(400 b) to the base station (400 c), whereby the mobile station (100)under communication, even during high speed movement, can continue acommunication successively through destination base stations without theneed of performing the handover operation, thus largely reducing thefrequency of the handover performed by the fast moving mobile station(100) under communication. In addition, the intervention of specialcontrol operations on the network side is not either required.

[0037] Further, when the mobile station (100) moves from the radio zone(200 a) to (200 b) and from (200 b) to (200 c) in succession at a highspeed, the radio signal delay control units (440) provided in therespective base stations (400 a)-(400 c) control the timing oftransmitting radio signals from the respective base stations (400a)-(400 c) to their subordinate radio transmission channels (300 a)-(300c) in accordance with values previously set for the respective basestations (400 a)-(400 c), such that a communication slot phase on theradio transmission channel (300 a) of the original base station (400 a)is synchronized with a communication slot phase on the radiotransmission channel (300 b) of the destination or adjacent base station(400 b) and also such that a communication slot phase on the radiotransmission channel (300 b) of the base station (400 b) is synchronizedwith a communication slot phase on the radio transmission channel (300c) of the adjacent base station (400 c), whereby the phases of thecommunication slots on the radio transmission channels (300 a)-(300 c)transmitted from the respective base stations (400 a)-(400 c), viewedfrom the fast moving mobile station (100) under communication, can beall synchronized with each other.

[0038] As described above, by synchronizing the communication slotphases with each other on the radio transmission channels (300 a)-(300c) over the respective radio zones (200 a)-(200 c), it is possible tolargely reduce noise or the like caused by communication slots fallinginto out-of-synchronization when the mobile station (100) moves from theradio zone (200 a) to (200 b) and from (200 b) to (200 c).

[0039] It will be appreciated from the foregoing that a precisecommunication quality can be ensured for the fast moving mobile station(100).

[0040] When the moving time of the mobile station (100) from the radiozone (200 a) to the radio zone (200 c) is estimated, if there is amobile station (100) moving at a speed different from a speed assumed asa moving speed of the mobile station (100), the conventional handoveroperation will be required at the timing a communication slot on theradio transmission channel (300 a) in the radio zone (200 a) istransferred to the radio transmission channel (300 b) in the radio zone(200 b) and from the radio transmission channel (300 b) to the radiotransmission channel (300 c) in the radio zone (200 c) and at the timinga communication slot on the signal line (500) is transferred from thebase station (400 a) to the base station (400 b) and from the basestation (400 b) to the base station (400 c). However, if a relativespeed |v-v1| between the assumed moving speed v and an actual movingspeed v1 of the mobile station (100) is equal to or less than a slowspeed of a vehicle at which the frequency of call interruptions due tothe handover operation is regarded to cause no problem, a degradation ofthe communication quality due to the call interruptions can besuppressed to a level at which a precise communication quality can beensured even in the conventional personal handy phone system. Forexample, assuming that the personal handy phone system according to thepresent invention is applied to highways with an assumed moving speed ofa mobile station (100) set at a fixed value of 80 km/h, a precisecommunication quality can be ensured if the relative speed of the mobilestation to this assumed moving speed is equal to or less than a slowspeed of a vehicle. Specifically, assuming that a slow speed of avehicle is approximately 30 km/h, if the mobile station runs at 50km/h-110 km/h or less, a precise communication quality can be ensured.

[0041]FIG. 4 is a diagram illustrating changes of the position of acommunication slot for a mobile station (100) in the process of time onradio transmission channels (300 a)-(300 c) in respective radio zones(200 a)-(200 c) in one embodiment of the personal handy phone systemaccording to the present invention.

[0042] Specifically, FIG. 4 illustrates by way of example that a secondslot on a radio transmission channel (300 a) at frequency f1 isallocated as a communication slot for the mobile station (100) in aradio zone (200 a) formed by a base station (400 a). In this case, anadjacent base station (400 b), installed in the middle of a movingdirection of the fast moving mobile station (100) under communication,allocates a second slot on the radio transmission channel (300 a) atfrequency f1 used by the mobile station (100) in the radio zone (200 a)to which the mobile station (100) has so far belonged, as acommunication slot for the mobile station (100) in the radio zone (200b) formed by the base station (400 b), at a timing (t1) at which apreviously estimated time period T has elaspsed. The time period T hasbeen set as a time period required for the mobile station (100) to movefrom the radio zone (200 a) to the radio zone (200 b). At the nexttiming (t2) at which another time period T has elapsed, the nextadjacent base station (400 c), installed in the middle of the movingdirection of the fast moving mobile station (100) under communication,allocates the second slot on the radio transmission channel (300 a) atfrequency f1 used by the mobile station (100) in the radio zone (200 b)to which the mobile station (100) has so far belonged, as acommunication slot for the mobile station (100) in the radio zone (200c) formed by the base station (400 c).

[0043] By performing similar operations in a chain manner along a movingroute of the mobile station (100), the fast moving mobile station (100)under communication is permitted to occupy the same slot at the samefrequency on radio transmission channels in destination radio zones insuccession.

[0044] Also, as the mobile station (100) moves from the radio zone (200a) to the adjacent radio zone (200 b) and further to the radio zone (200c) in succession at a high speed, the radio signal delay control units(440) provided in the respective base stations (400 a)-(400 c) controlthe timing of transmitting radio signals to the respective subordinateradio transmission channels (300 a)-(300 c) from the base station (400a)-(400 c) in accordance with previously set values for the basestations (400 a)-(400 c), whereby the phases of the communication slotson the radio transmission channels (300 a)-(300 c) transmitted from therespective base stations (400 a)-(400 c), viewed from the fast movingmobile station (100) under communication, can be all synchronized witheach other.

[0045]FIG. 5 is a diagram illustrating changes, in the process of time,of the position of a communication slot for a mobile station (100)occupying on a signal line in the respective base stations (400 a)-(400c) installed along a moving route of the mobile station (100) in oneembodiment of the personal handy phone system according to the presentinvention.

[0046] Specifically, FIG. 5 illustrates by way of example that in a basestation (400 a), a second slot on a line No. 1 is allocated as acommunication slot on the signal line (500) for the mobile station(100). In this case, an adjacent base station (400 b), installed in themiddle of a moving route of the fast moving mobile station (100) undercommunication, allocates a second slot at a line No. 1 used by themobile station (100) in the base station (400 a) to which the mobilestation (100) has so far belonged, as a communication slot for themobile station (100), at a timing (t1) at which a previously estimatedtime period T has elapsed. The time period T has been set as a timeperiod required for the mobile station (100) to move from the radio zone(200 a) to the radio zone (200 b). At the next timing (t2) at whichanother time period T has elapsed, the next adjacent base station (400c), installed in the middle of the moving route of the mobile station(100), allocates the second slot on the line No. 1 used by the mobilestation (100) in the base station (400 b) to which the mobile station(100) has so far belonged, as a communication slot for the mobilestation (100).

[0047] By performing similar operations in a chain manner along themoving route of the mobile station (100), the fast moving mobile station(100) under communication is permitted to occupy the same slot at thesame frequency on the same signal line in the destination base stationsin succession.

[0048] As described above, a fast moving mobile station (100) undercommunication is permitted to continue a communication successivelythrough destination base stations without requiring the intervention ofspecial processing controls on the network side or without performingany handover operation required by the fast movement of the mobilestation (100). In addition, since all the phases of communication slotson the radio transmission channels transmitted from the respective basestations can be synchronized with each other, it is possible to realizethe insurance of a precise communication quality with less callinterruptions and less introduced noise even during the fast movement ofthe mobile station.

[0049]FIG. 6 shows a comparison between a conventional personal handyphone system and the personal handy phone system according to thepresent invention in terms of a processing sequence between a mobilestation and base stations when the mobile station switches a radio zoneto which it belongs.

[0050] As shown in FIG. 6, the-conventional personal handy phone systemrequires a re-call handover operation for switching a radio zone towhich a mobile station belongs. More specifically, since a sequence of alink channel establishment request, a link channel allocation, a callsetting, a call setting reception and a response is required between themobile station and a destination base station, a call is interruptedduring the execution of this sequence. On the other hand, the personalhandy phone system of the present invention need not perform thehandover operation as mentioned above and accordingly does not requirethe sequence of operations associated with the handover operation, sothat no interruption occurs in a call during the switching of a radiozone to which a mobile station belongs.

[0051]FIG. 7 represents a flow of specific operations performed by eachbase station in the personal handy phone system according to the presentinvention. Specifically, this flow shows a processing flow in anarbitrary base station within a plurality of base stations installedalong a moving direction of a mobile station.

[0052] A control unit in the base station acquires, through a signalline (500), information on a frequency of a radio transmission channeland the position of a communication slot on the radio transmissionchannel used by a mobile station dominated by an adjacent base stationlocated in the direction opposite to the moving direction of the mobilestation, i.e., a preceding adjacent base station from which the mobilestation is moving thereto, and information on a signal line number andthe position of a communication slot on the signal line (step F1).

[0053] A required time period (particular fixed value) for the mobilestation to move between adjacent radio zones is calculated from anassumed moving speed (particular fixed value) of the mobile station andthe installation interval of base stations (400 a)-(400 c), andcommunication slots for each mobile station on a radio transmissionchannel and on a signal line is transferred between the respective basestations for switching a radio zone to which the mobile station belongsat the timing at which the estimated moving time has elapsed. Thus, thecontrol unit in the base station monitors the arrival of the radio zoneswitching timing (the lapse of a particular fixed time period) (stepF2).

[0054] When the radio zone switching timing has reached, the controlunit in the base station controls a radio channel allocating functionunit and a signal line allocating function unit to release communicationslots occupied on the radio transmission channel and on the signal lineused for a mobile station which has so far belonged to the associatedradio zone (step F3).

[0055] The control unit in the base station controls the radio channelallocating function unit to allocate the same slot on the radiotransmission channel at the same frequency as a communication slot forthe mobile station which has moved into the radio zone covered by thebase station, in accordance with the information acquired at step (F1)on the frequency of the radio transmission channel and the position ofthe communication slot on the radio transmission channel used by themobile station when dominated by the preceding adjacent base station(step F4).

[0056] The control unit in the base station controls the signal lineallocating function unit to occupy the same slot on the same signal lineas a communication slot for the mobile station which has moved into theradio zone covered by the base station, in accordance with theinformation acquired at step (F1) on the signal line number and theposition of the communication slot on the signal line used by the mobilestation when dominated by the preceding adjacent base station (step F5).

[0057] A radio signal delay control unit in the base station delays atransmission timing by a previously adjusted set time period so as tosynchronize the phase of the communication slot on the radiotransmission channel with that of the adjacent base station, when thebase station sends the communication slot onto the radio transmissionchannel for the mobile station which has come into the radio zonecovered by the base station (step F6).

[0058] A modulator/demodulator unit modulates a radio signal having thetransmission timing delayed by the adjustment to be sent to the radiotransmission channel, and the modulated signal is sent onto the radiotransmission channel from a radio signal transmitter/receiver unitthrough an antenna (step F7.

[0059] Subsequently, the flow returns to step F1 to repeat the procedureof steps F1-F7.

[0060] According to the foregoing embodiment, it is possible to suppressoccurrence of the handover operation performed in a fast moving mobilestation under communication, thereby making it possible to reduce callinterruptions caused by the handover operation and to realize theinsurance of a precise communication quality for the fast moving mobilestation in the mobile radio communications system.

1. A mobile radio communications system having a plurality of basestations accommodating a plurality of mobile station through radiotransmission channels, each said mobile station connected with a mobilecommunications exchanger through a plurality of signal lines, each ofsaid signal lines parallelly connected to said plurality of basestations, each said base station including a mechanism of selecting aparticular signal line from said plurality of signal lines andallocating a communication slot for a mobile station dominated by saidbase station at a particular slot position on the selected signal line,and a mechanism of allocating a communication slot for the mobilestation dominated by said base station at a particular slot position ofa radio transmission channel at a particular frequency, wherein: eachsaid base station autonomously allocates a frequency of a radiotransmission channel and a time slot on the radio transmission channelused by a mobile station dominated by said base station, when saidmobile station was dominated by an adjacent base station, for saidmobile station dominated by said base station, in accordance with alapse of a fixed time period calculated from a previously assumed movingspeed of a moving mobile station under communication; each said basestation allocates a signal line and a communication slot on said signalline used by said mobile station dominated by said base station, whensaid mobile station was dominated by the adjacent base station, for saidmobile station dominated by said base station; and said moving mobilestation sequentially switches a base station to which said moving mobilestation is connected, among said plurality of base stations installedalong a moving direction of said moving mobile station undercommunication, without performing a handover operation.
 2. A mobileradio communications system according to claim 1, wherein each said basestation further comprises radio signal delay control means capable ofvariably setting a delay time for a transmission timing when each saidbase station transmits a signal to a mobile station accommodated in anassociated radio zone associated with said base station, so that whensaid respective base stations transmit digital modulated signals to amobile station, said respective base stations mutually match the phasesof their time-division multiplexed channel slots allocated fortime-division multiplexed digital modulated signals sent from saidrespective base stations onto associated radio transmission channels andtransmitted to said mobile station.
 3. A method of switching a radiozone for a mobile radio communications system having a plurality of basestations accommodating a plurality of mobile station through radiotransmission channels, each said mobile station connected with a mobilecommunications exchanger through a plurality of signal lines, each ofsaid signal lines parallelly connected to said plurality of basestations, each said base station including a mechanism of selecting aparticular signal line from said plurality of signal lines andallocating a communication slot for a mobile station dominated by saidbase station at a particular slot position on the selected signal line,and a mechanism of allocating a communication slot for the mobilestation dominated by said base station at a particular slot position ofa radio transmission channel at a particular frequency, said methodcomprising the steps of: autonomously allocating, in each said basestation, a frequency of a radio transmission channel and a time slot onthe radio transmission channel used by a mobile station dominated bysaid base station, when said mobile station was dominated by an adjacentbase station, for said mobile station dominated by said base station, inaccordance with a lapse of a fixed time period calculated from apreviously assumed moving speed of a moving mobile station undercommunication; allocating a signal line and a communication slot on saidsignal line used by said mobile station dominated by said base station,when said mobile station was dominated by the adjacent base station, forsaid mobile station dominated by said base station; and sequentiallyswitching a radio zone to which said moving mobile station undercommunication belongs, without performing a handover operation, whensaid moving mobile station under communication passes through saidplurality of base stations installed along a moving direction of saidmoving mobile station under communication.
 4. A base station for amobile radio communications system comprising: an antenna; a radiosignal transmitter/receiver unit; a modulator/demodulator unit; a radiosignal delay control unit for providing a transmission timing with adelay of a previously set time period when a digital signal receivedfrom a mobile communications exchanger and destined to a mobile stationdominated by said base station is modulated by saidmodulator/demodulator unit and transmitted from said radio signaltransmitter/receiver unit through said antenna to said mobile stationdominated by said base station; a radio channel allocating function unitfor selecting a particular frequency as a radio transmission channel fortransmitting and receiving a radio signal to and from a mobile station;a signal line allocating function unit for selecting a particular signalline from a plurality of signal lines as a signal line for transmittingand receiving a digital signal to and from said mobile communicationsexchanger and for allocating a communication slot for said mobilestation dominated by said base station at a particular slot position onsaid selected signal line; and a control unit for generally controllingsaid radio signal transmitter/receiver unit, said modulator/demodulatorunit, said radio signal delay control unit, said radio channelallocating function unit, and said signal line allocating function unit.